Studies will continue on the biochemical development of surface activity of lung of the developing fetus, including man. Investigations will continue of the enzymatic synthesis of the surfact active phospholipids, under normal and abnormal physiological conditions (hypoxia, acidosis, hypercarbia). Recent studies on an important "minor" phospholipid, phosphatidyl glycerol (PG), will be expanded, especially since surfactant maturation seems to be dependent upon PG synthesis. The relation in surfactant between PG and phosphatidyl inositol will be further explored. Using the amniotic fluid phospholipid lecithin/sphingomyelin (L/S) ratios as the marker of fetal lung maturity, investigations will continue about the mechanisms whereby maternal, fetal and placental conditions influence maturity of fetal lung. The regulatory mechanisms involved are being studied in normal pregnancy and in animal pregnancies stressed experimentally.